Renal transplantation affords patients with end stage renal disease an improved quality of life and spares them from life-long dialysis and its complications. Approximately 30-40% of transplant recipients suffer at least one episode of acute graft dysfunction, and half of those experience repeated events. Causes include surgical complications related to vascular and ureteral anastomoses and intrinsic pathology such as acute tubular necrosis, rejection, and drug toxicity. Existing protocols for monitoring grafts rely on insensitive measures such as serum creatinine, and clinical differentiation between causes of dysfunction, particularly intrinsic diseases is difficult. Biopsy is frequently required. Magnetic resonance imaging (MRI) offers the unique potential to combine anatomic evaluation of transplants with a functional assessment using glomerular contrast agents such as Gd- DTPA. High resolution Gd-enhanced MR renography, when interpreted using tracer kinetic analyses, can noninvasively detect and differentiate vascular, glomerular, and tubular pathologies, and by reflecting changes seen at histopathology may enable accurate diagnosis of intrinsic renal diseases. Broad, long-term objectives: To improve renal graft survival by developing a noninvasive test that can be used to monitor and diagnose graft dysfunction. A test that can accurately distinguish intrinsic causes of disease would ensure prompt and appropriate therapy and help to obviate invasive biopsy procedures. Specific Aims/Methods: (1) To determine diagnostic criteria for quantitative MR renography, analyzed using a tracer kinetic model of the vascular-nephron system, to diagnose patients with acute renal transplant dysfunction. (2) To develop semi-automated image processing and data analysis methods for MR renography of renal transplants that will be enable routine clinical implementation of MR renography in the clinical setting. (3) To apply and test quantitative MR renography criteria, as determined in (1), for the diagnosis of patients with acute renal transplant dysfunction. At its conclusion, our study has a high likelihood of showing that functional MR renography for differentiating intrinsic renal diseases, will be an accurate tool for acute renal transplant dysfunction.